20051014

Quantum Time Machines: What, Why and How?Queensland/Tokyo Tim Ralph presents a Qulink seminar on closed timelike curves in context of quantum information processing. "Whether time travel into the past is possible is an undecided physical question. Recently it has been noted that certain models of time travel for quantum particles do not lead to the same difficult paradoxes that arise for classical particles. Furthermore the types of quantum evolutions predicted for these 'quantum time machines' could give rise to a 'super' quantum computer, able to solve problems thought to be intractable by any other means. In this talk I will discuss time machines in general, how quantum mechanics avoids the paradoxes and the unusual evolutions predicted. I will then argue that the requirements for realizing such machines are not as stringent as previously thought and I will propose "horizon technology" experiments which could test these ideas."

Theoretical and Experimental Exploration of Time Reversal Formalism Applied to EntanglementIQC, Waterloo In quant-ph/0510048, Laforest, Laflamme and Baugh investigate time reversal of the Schrodinger equation in the context of teleportation. Experimental results are consistent with the interpretation that information can be seen as flowing backward in time through entanglement. "In this paper, we analyze whether the acausal flow of information in a teleportation protocol can actually be physical, or should only consist of a mathematical model. Using an NMR spectrometer, we have demonstrated experimental results faithful with the interpretation that, conditionally and in principle, entanglement seems like it can break the causality of time."

RSFQ Circuits with Selective Dissipation for Coherent Quantum Information ProcessingVTT, Finland RSFQ, or rapid single flux quantum logic serves as a central component of HTMT, hybrid technology multi-threaded computing and other prototype high-performance architectures. In cond-mat/0510189, Hasselet al. investigate frequency-dependent damping as a means to reduce dissipation and subsequent decoherence in Josephson junction RSFQ/qubit circuits. "We derive criteria for the stability of such an arrangement, and discuss the effect on decoherence and the optimisation issues. We also design a simple flux generator aimed at manipulating flux qubits."